We have measured the electrical and optical properties of blue light-emitting diodes ͑LEDs͒ based on III-V nitrides. The current-voltage characteristic is described by means of the relation IϭI 0 exp(␣V). In this equation ␣ is temperature independent, suggesting a process of conduction by tunneling, as was recently reported also for blue-green LEDs based on III-V nitrides ͓Appl. Phys. Lett. 68, 2867 ͑1996͔͒. We explain the differences between blue and blue-green devices taking into account the tunneling process across semiconductor interfaces, in which a great number of defects is present. The light output intensity of the LED as a function of junction-voltage data reveals a dependence on the junction-voltage of the type LϭL 0 exp͑qV/1.4 KT͒, indicating that the radiative recombination path is via deep levels located at the forbidden gap. Furthermore, we find that the light output-current characteristic follows a power law like LϰI p . From the analysis of data it appears that, contrary to expectations, the nonradiative centers are saturated at very low current values that are comparable to the values at which this saturation takes place in LEDs based on III-V arsenides with a low content of defects. © 1997 American Institute of Physics. ͓S0021-8979͑97͒05304-8͔Blue light-emitting diodes ͑LEDs͒ based on III-V nitrides have recently shown high brightness characteristics 1 in spite of the presence of an extremely high density of dislocations ͑in the 2-10ϫ10 10 cm Ϫ2 range 2 ͒ that is several orders of magnitude higher than those measured in LEDs based on III-V arsenides and phosphides. Blue and blue-green devices are commercially available from Nichia Chemical Industries. 1,3 The main difference between them is the composition of the active layer ͑In 0.06 Ga 0.94 N for blue devices and In 0.23 Ga 0.77 N for the blue-green emitters͒.Here, we present a study of the influence of defects on the transport properties and on the optical characteristics of the Nichia blue LEDs and we compare the results with those reported in blue-green LEDs from the same manufacturer. 4 The blue LED analyzed in this study is device part No. NLPB500. The physical structure is composed of different layers, all of them grown by metalorganic chemical vapor deposition ͑MOCVD͒. Briefly, the structure is as follows: a n-GaN bottom contact layer ͑ϳ4 m͒, followed by a double heterostructure ͑DH͒ composed of an n-Al 0.15 Ga 0.85 N carrier confinement layer ͑ϳ0.15 m͒, an In 0.06 Ga 0.94 N active layer, Si and Zn codoped ͑0.05 m͒, and a p-Al 0.15 Ga 0.85 N carrier confinement layer ͑0.15 m͒. Last is a p-GaN top contact layer ͑0.5 m͒.We have measured the current-voltage (I -V) characteristic and the light output intensity as a function of junctionvoltage (L -V) and LED output current (L -I). The I -V and L -V data are influenced by the presence of a series resistance at high voltages. We have suppressed this influence following the procedure described in Ref. 5. Over the entire current range, where the influence of series resistance is present ͑4ϫ10 Ϫ...

We present a laboratory experiment to show the current - voltage (I - V), light output - voltage (L - V) and light output - current (L - I) characteristics of light-emitting diodes (LEDs) and semiconductor laser (SLs). The experiment allows us to compare the processes of light emission in LEDs and lasers below the threshold (spontaneous emission) and above it (stimulated emission). We establish unambiguously the analogies of the characteristics of LED emission in comparison with laser emission, when this occurs in the regime of spontaneous emission. We also determine the differences between LED and laser operation (when this occurs in the regime of stimulated emission) in a different way than that usually found in textbooks. Resumen. En este trabajo se presenta un sistema experimental destinado a mostrar las relaciones entre las caracteristicas I - V, L - V y L - I de diodos emisores de luz (LED) y láseres de semiconductor. La experiencia permite comparar los procesos de emisión de luz de los LEDs y láseres por debajo del umbral (emisión espontánea) y por encima de él (emisión estimulada). Mostramos de forma clara las analogías entre el LED y el láser en la zona de emisión espontanea. Cuando el láser trabaja en la zona de emisión estimulada, las diferencias se caracterizan de forma distinta a la habitual de los libros de texto.

We present a laboratory experiment designed to show the main characteristics of blue light-emitting diodes. The analyzed devices are based on III-V nitrides ͑in which the active layer is a direct band gap In 0.06 Ga 0.94 N alloy͒ and SiC ͑where the active layer is the 6H polytype of this semiconductor, which is of an indirect band gap class͒. From the measurements, an I n relation could be established between light emission and device current, with n values related to both the physical structure and electroluminescence characteristics of these semiconductors. The spectral response measurements allow us to obtain the peak wavelength of emission with reasonable precision ͑449Ϯ4 nm in the former one and 470Ϯ4 nm in the last one͒. It is also possible to accurately obtain the band gap value of the active layer in the device based on III-V nitrides ͑3.18Ϯ0.03 eV͒ by analyzing its electroluminescence spectra. However, the same analysis is not possible in the SiC-based device due to its extremely low measured luminous intensity values. A comparison of power conversion efficiency of both devices is also given. ©